1. Field of the Invention
This invention relates to an inorganic solid electrolyte glass phase composite and a battery having an inorganic solid electrolyte glass phase composite. Specifically, this invention relates to a lanthanum lithium titanium oxide glass phase composite. The glass phase is preferably an aluminum oxide or a boron oxide. The inorganic solid electrolyte glass phase composite may be used in lithium-ion batteries, thin film batteries, pH sensors, and separation devices. A battery having a lanthanum lithium titanium oxide glass composite solid electrolyte is also provided.
2. Description of the Background Art
Lithium-ion conducting solid electrolytes (Li-CSEs) are known and provide advantages over traditional liquid electrolytes, such as thermal stability, absence of leakage, resistance to physical vibrations, larger electrochemical applications and ease of miniaturization. Generally, Li-CSEs are classified into two categories: oxides and sulfides. To date, sulfide based Li-CSEs are considered superior to oxide-based Li-CSEs in their total ionic conductivity. While the sulfide based Li-CSEs to date have been preferred over the oxide based LiCSEs, the sulfide based Li-CSEs are difficult to synthesize. Oxide based Li-CSEs are relatively easy to synthesize and are generally resistive to moisture. Prior to the present invention, the oxide based Li-CSEs of the perovskite-type lithium lanthanum titanium oxide have achieved a bulk conductivity σb of 2.95×10−3 S cm−1 at 295 Kelvin (K), however, they have significant obstacles to their utilization, including for example, poor ionic conduction of its grain boundary leading to a low total ionic conductivity, chemical instability in direct contact with elemental lithium, and a very narrow electrochemical window (1.7 volts), among others. To overcome these obstacles of the oxide-based Li-CSEs, it is known by those persons skilled in the art to coat the oxide based Li-CSEs of the perovskite-type lithium lanthanum titanium oxide with low melting Li-CSE Li3.25Ge0.25P0.75S4 (hereinafter Li-CSE LGPS) resulting in a sulfide/oxide composite electrolyte having a total ionic conductivity as high as 1.62×10−4 S cm−1 and a low electronic conductivity of 2.38×10−9 S cm−1 at room temperature. This Li-CSE LGPS coating procedure however adds to the manufacturing expense of producing an oxide based Li-CSEs of the perovskite-type lithium lanthanum titanium oxide. U.S. Pat. No. 6,277,524 discloses a lithium-ion solid electrolyte including a lithium-ion conductive substance with the general formula Li2S—GeS2—X wherein X is selected from the group consisting of Ga2S3 and ZnS or Li2S—SiS2—P2S5.
Prior to the present invention, the conductivity of grain boundary and chemical stability limited the practical application of LLTO. It is known that the total conductivity for LLTO is limited by the effect of grain boundaries, which is in the order of 10−5 S cm−1 and about two orders lower than that of grain inside. Numerous investigators have tried to improve the conducting properties of LLTO by substituting La and/or Ti with other metal ions. For example, Ainhoa Morata-Orrantia et al., “Optimization of Lithium Conductivity in La/Ti Titanates”, Chemistry of Materials, Vol. 15, pages 3991-3995 (2003), made an improvement on the ionic conductivity to σbulk=2.95×10−3 Scm−1 for La0.56Li0.33TiO0.07Al0.03O3 in comparison with σbulk=1.32×10−3 Scm−1 for La0.56Li0.33TiO3. Further, the addition of a second phase has been investigated by others to demonstrate the effect of an inactive phase on the conductivity for Li-ion transport. For example, Yuan Deng et al., Journal of Alloys and Compounds, Vol. 472, pages 456-460 (2009) improved the grain boundary conductivities through the addition of SiO2 to form Li0.5La0.5TiO3/inactive second phase composites.
As a solid electrolyte for Li-ion batteries, La2/3-xLi3xTiO3 (hereinafter “LLTO”) has not been commercialized mainly due to the following problems: (i) low ionic conductivity at the grain boundaries, and (ii) low chemical stability in contact with the anode of Li-ion batteries. Thus there is an identifiable need to create an improved oxide based Li-CSEs of the perovskite-type lithium lanthanum titanium class, and specifically an inorganic solid electrolyte LLTO composite. In spite of this background art, there remains a very real and substantial need for (i) an improved inorganic solid electrolyte composite having an improved LLTO, (ii) an improved lithium-ion conductive solid electrolyte composite having a lithium-ion conductive substance having a LLTO composite, and (iii) a battery having a cathode, an anode, and an improved inorganic solid electrolyte LLTO composite disposed on or between the cathode and anode.